When a rechargeable lithium battery is charged, a potential gap between a positive electrode and a negative electrode occurs at initial charging. Such potential gap allows a surface of the negative electrode to react with an electrolyte, thereby producing a solid electrolyte interface (SEI) film on the surface of the negative electrode. The SEI film helps to intercalate and deintercalate lithium ions into the negative electrode. However, decomposition of the electrolyte, which is a side reaction simultaneously occurs, which generates gas, thereby raising the internal pressure of the battery. As a result, a swelling phenomenon occurs in which the battery thickens, the battery capacity is reduced, and it is difficult to produce various types of batteries in rectangular shapes because of the distortion.
Therefore, various attempts to prevent gas generation have been attempted.
One, attempt involves adding to the electrolyte an additive that has previously decomposed. This reduces the amount of generated gas, but the effects are insufficient because the reaction between the additive and the negative electrode occurs unevenly because of the morphology of the porous negative electrode. Furthermore, the additive concentrates on a surface of the negative electrode and actively contacts the electrolyte so that lithium metal deposit on the surface of the negative electrode by an over potential thereof. This causes an abrupt deterioration of battery performance factors such as cycle life and high-rate and low-temperature characteristics. This also makes it difficult to form the SEI film on the surface of the negative electrode, and it causes the battery to be unstable.
Another attempt involves gas removal by initial-charging a battery under an inert atmosphere. However, this method has a shortcoming in that it is not economical due to additional equipment for initial charging being required.